The percutaneous absorption of indomethacin (ID) from five kinds of fatty alcohol and propylene glycol (FAPG) bases consisting of a mixture of fatty alcohol (FA) and propylene glycol (PG) was studied by using the depilated abdominal skin of rats. The percutaneous absorption of ID from No. 1 base consisting of stearyl alcohol (SOH) and 75% of PG was slightly higher than that of No. 2 base consisting of SOH and 66.7% of PG. The absorption of ID from No. 3 base consisting of SOH and 50% of PG was significantly lower than those of Nos. 1 and 2 bases. It became evident that the amount of ID absorbed in cutis from FAPG base and the release rate of ID in vitro tended to increase as the content of PG in FAPG increased. Furthermore, in Nos. 1, 2, and 3 FAPG bases, it was observed that the viscosity of base also exerted an influence on the percutaneous absorption and release rate of ID. The viscosity of No. 4 base consisting of cetyl alcohol (COH) and 75% of PG was almost the same as No. 1 base, whereas the percutaneous absorption of ID from the former was lower than that of the latter. The viscosity of No. 5 base consisting of SOH and COH (a mixing rate of 1 : 1) and 75% of PG was higher than that of No. 4 vase. However, the percutaneous absorption of ID from both bases was almost the same. It was found that the percutaneous absorption of ID from FAPG base containing different kinds of FA in a given volume of PG was not affected by the viscosity of base. Moreover, it was cleared from further experiment that the partition ratio of ID between water and FAPG base exerted an influence on the percutaneous absorption of ID.
